With direct vent gas fireplaces, it is preferred to minimize the clearance required between the unit and combustible materials. The ideal is "zero clearance". To achieve this, fireplaces have been constructed with wrappings of thermal insulation and plural circulation chambers around the firebox. The air chambers heat room air as well as providing insulation. This increases the overall size of the fireplace, making the unit project some distance into a room when installed in a standard stud wall.
Conventional direct vent gas fireplace design has been either a top vent or back vent configuration. Recently, units with sloped top walls oriented at 45.degree. to horizontal have been proposed so that a 45.degree. elbow can be used to produce either a top vent or a back vent arrangement using the same unit. With the top vent arrangement, it is found that the position of the vertical run of the combustion air duct limits the depth to which the unit may be installed in a wall. This is not a significant problem with conventional fireplace designs. If however, the depth of the unit is reduced, it becomes a limiting factor.
The present invention is concerned with certain improvements in direct vent gas fireplaces.